Most every centrifugal pump has a peak efficiency point which can be plotted on a performance curve of flow rate versus efficiency. When the centrifugal pump operates at a condition off of the peak efficiency point, it creates pre-rotation and back-flow conditions. A pre-rotation or pre-swirl condition is the mismatch between incoming fluid flow and the rotation of the impeller inlet blades. Back-flow is a phenomena which occurs when flow reverses around the inducer's leading edge in a swirling motion back down the inlet piping. These characteristics of the pump inlet flow reduce the overall pump performance, due to excess work done on the fluid by the impeller blades, and the increased air in the inlet line, in essence, reduces the inlet area for the pump liquid, such as a fuel.
If the swirling problem can be reduced or stopped by some means, the pump capabilities will increase. One solution is to provide a deswirl vane or splitter vane means in the pump inlet. This drastically increases the performance of the pump by reducing the swirling in the inlet.
It is desirable with most such centrifugal pumps of the character described to construct the pump so that the impeller means, blades, etc. are readily removable for maintenance, repair or replacement. Therefore, it is desirable to provide a shut-off valve means to close the inlet when the impeller means are removed.
Providing these desirable features of anti-swirl vane means and shut-off valve means in centrifugal pump systems creates problems due to envelope and maintenance constraints placed on pump designs, such as the overall length of the pump, i.e., the pump envelope. This is particularly critical in the aircraft or aerospace field. Splitter vanes take up considerable space within the envelope. In addition, the most efficient shut-off inlet valve design is a bi-petal design which has petal valves that swing about a radius which is within the envelope. Obviously, providing all these features in a single pump design can substantially increase the envelope size.
This invention is directed to solving this dilemma by providing a new and improved anti-swirl vane and shut-off valve system of an extremely compact design while still performing the desirable functions.